Conformational Regulation of Multivalent Terpyridine Ligands for Self-Assembly of Heteroleptic Metallo-Supramolecules

A two-ligand system composed of the predesigned multivalent and complementary terpyridine-based ligands was exploited to construct heteroleptic metallo-supramolecules and to investigate the self-assembly mechanism. Molecular stellation of the trimeric hexagon [Cd₆L₃] gave rise to the exclusive self-assembly of the star hexagon [Cd₁₈L₆L₃] through complementary ligand pairing between the ditopic and octatopic tectons. To understand how the intermolecular heteroleptic complexation influenced the self-assembly pathway, the star hexagon was truncated into two triangular fragments: [Cd₁₂L₃L₃] and [Cd₁₂L₃L₃]. In the self-assembly of [Cd₁₂L₃L₃], the conformational movements of hexatopic ligand L could be regulated by L to promote the subsequent coordination event, which was the key step to the successful multicomponent self-assembly. In contrast, the formation of [Cd₁₂L₃L₃] was hampered by the geometrically mismatched intermediates.